During continuous reeling of paper in a reel-up in a modem paper machine, very stringent demands as regards strength are made on the reel spools on which the paper web is wound to form jumbo rolls. A modern paper machine produces paper with a web speed of several thousand meters per minute, and the width of the paper web in such machines is ordinarily in the range 2.5-8 meters. Accordingly, the reel spools must be sturdily dimensioned to withstand the weight of the paper roll and the rotational speed required by the web speed. The demands made on a reel spool in the reel-up of a paper machine are thus completely different from the demands made on reel spools occurring in machines for subsequent processing of the paper roll, for instance rewinders and slitter-winders.
To meet the requisite demands for strength, known types of reel spools comprise a hollow steel reel spool. At its ends, the steel reel spool usually has protruding shaft journals, intended to support the steel reel spool rotatably in the reel-up. In a common type of reel shaft, a paper core is detachably attached to the envelope surface of the steel reel spool by means of a locking device. Thus, the steel reel spool acts as a support shaft for the paper core and, once the paper web has been wound onto the reel spool, the locking device is disengaged from the paper core, whereupon the steel reel spool is extracted from the paper core with the aid of an extraction device. The exposed steel reel spool is thereupon provided with a new paper core and returned to a nearby stock of steel reel spools provided with paper cores to be used in a subsequent reeling sequence. Accordingly, the paper core forms the core of the wound paper roll and thus accompanies the wound paper to subsequent processing procedures. When the paper core in due course is disengaged from the paper during such a processing procedure, for instance during rewinding of the paper roll, an uncovered steel reel spool is inserted into the paper core and thereafter placed in the stock of steel reel spools provided with paper cores for the reel-up.
It is known to cover the steel reel spool with a composite core of fiber-reinforced plastic instead of a paper core. Whereas a paper core must usually be discarded after about three reeling cycles, that is after being mounted on and removed from steel reel spools three times, a plastic composite core has a virtually unlimited service life.
Another type of reel spool is described in U.S. Pat. No. 3,743,199, which, in common with the spindle described above, consists of a steel reel spool, having protruding shaft journals at its ends, intended to support the reel spool rotatably in the reel-up. Unlike the reel spool described above, however, the paper is in this case wound directly onto the envelope surface of the steel reel spool. In addition, at least one of the shaft journals exhibits a channel running axially through the same and communicating with the hollow interior of the steel reel spool, and the envelope surface of the steel reel spool exhibits a plurality of evenly distributed holes running through the same and likewise communicating with the hollow interior of the steel reel spool. When the paper web is to be wrapped around the empty steel reel spool in the initial phase of the reeling, a vacuum pump is connected to the shaft journal exhibiting the through-running channel, or to both shaft journals if both shaft journals exhibit through-running channels, to generate a negative pressure inside the steel reel spool. The negative pressure creates a flow of air in through the holes in the envelope surface of the steel reel spool, which flow of air unsettles the film of air surrounding the paper web so that the paper web can be adjoined to the steel reel spool more easily, thereby facilitating the wrapping of the paper web on the steel reel spool. In this case, however, the steel reel spool must accompany the wound paper to subsequent processing procedures, as the steel reel spool cannot normally be withdrawn from the paper roll without difficulties. When the paper in due course is unreeled from the steel reel spool, the same is returned to the stock of steel reel spools in the reel-up to be used in a subsequent reeling sequence.
Using a reel spool comprising a steel reel spool entails numerous problems, however. As previously mentioned, a reel spool must be dimensioned to satisfy predetermined strength criteria, and, because of the strength criteria, the steel reel spool must be fashioned with a large diameter and substantial material thickness. Consequently, a conventional reel spool has considerable mass and a great moment of inertia with respect to its rotational axis. This makes it very difficult to balance a conventional reel spool and it is almost inevitable that the reel spool must exceed at least one rotational speed that is critical as regards self-oscillation to achieve normal rotational speed for reeling. This subjects both the reel-up and the reel spool to very considerable mechanical stress. Moreover, irrespective of said self-oscillation, the great mass and moment of inertia of the conventional reel spool require the reel-up to have sturdy dimensions to support, control, accelerate, and decelerate the reel spool. The great mass of the conventional reel spool also makes it very difficult to regulate the linear load in the paper web, especially in the initial phase of the reeling, as the weight of the reel spool greatly outweighs the linear load. A further problem arises in such cases where the finished paper roll rests on a plane surface with the reel spool still in place at the center of the paper roll, as sometimes occurs. In such cases, the paper roll can be deformed under the weight of the reel spool. This is a problem particularly in the manufacture of soft crepe paper, where costly additional equipment is necessary to relieve the mass of the reel spool so that the paper roll is not damaged by compression. Besides, the target aimed at in the current trend, especially in the manufacture of soft crepe paper, is ever higher web speeds, which, to satisfy strength requirements, necessitates steel reel spools with ever greater diameters and that are ever more rigid and heavy, which accentuates the above-mentioned problems.
A further problem can arise when using a reel spool of the type described above, which is that a gap can arise between the steel reel spool and the paper or plastic composite core covering the steel reel spool during reeling. When such a gap arises, balancing faults occur, which make it difficult to regulate the linear load. This is a problem particularly when using paper cores, as paper cores can be difficult to manufacture within the margins of tolerance that ensure a good fit between the paper core and the steel reel spool. Further, paper cores are not particularly stable in shape, which means that they can lose their original shape during the course of processing.
Another problem additionally arises in the reel spool described in U.S. Pat. No. 3,743,199. The shaft journals and their fastenings in the steel reel spool must be sturdily dimensioned, because of the weight of the steel reel spool. In reel spools of this type, the cross-sectional area of the channel in the shaft journal through which air is extracted from the hollow interior of the steel reel spool is therefore small relative to the cross-sectional area of the channel forming the hollow interior of the steel reel spool. As the limited cross-sectional area of the channel in the shaft journal constitutes an obstacle to the flow of air, it can be difficult to achieve the desired negative pressure inside the steel reel spool during the initial wrapping.